Next-Generation Wooden Racket

ABSTRACT

The invention relates to a tennis racket including a frame, delimiting a surface strung with cords and forming a screen, and a sleeve extending the frame outside the screen, characterized in that the frame consists of, at least within a peripheral region, a curved laminate comprising at least two layers of different materials adhered together, the laminate being shaped such that, in a closed cross-section of said peripheral region considered to be perpendicular to the neutral fiber of the frame, the center of mass of said cross-section is offset, relative to the surface center of gravity of said cross-section, toward the screen with a value at least equal to 5% of the width of said cross-section, said width being defined by the intersection of the cross-section and the plane of the screen.

The invention relates to the field of rackets for sport or various ball games. For the sake of convenience, the term “tennis rackets” will be used hereinafter as the main, non-limitative, illustration of the invention. The invention can also apply to other types of-racket, for example squash rackets or any other racket with a mesh delimited by a rigid frame.

Tennis rackets have undergone numerous technical developments over time. Early generations of racket were made from wood and naturally derive from the predecessor of tennis, jeu de paume. In the 1930s, new wood adhesives made it possible to produce glued-laminated rackets with several types of wood (ash, walnut, beech, maple). These could withstand greater stresses and provided a better balance between power and ball control.

New materials had to appear before there would be a revolution in the world of rackets. Gradually, metal (steel, aluminium, etc.) appeared in the 1970s. However, metal rackets enjoyed only limited success. From the 1980s onwards, synthetic fibres (carbon, fibreglass blend, etc.) made it possible to produce rackets that were both light and powerful. These new materials replaced wooden rackets which, due to their structure and composition, could not rival the performance of the new materials. Wooden rackets almost completely disappeared during the 1980s.

However, these technological advances prematurely cast aside wood, which is a natural material that fits perfectly with an eco-design approach that is very well perceived by users, and also has remarkable technical properties that can rival synthetic or processed materials, provided that the correct wooden structure or composition is found for producing racket frames.

The object of the present invention is to propose a new racket made principally from wood that uses a large proportion of natural and renewable materials, while offering comparable performance to rackets made from synthetic materials, which currently occupy the entire market or almost the entire market.

To this end, the invention relates to a racket for ball games, particularly tennis, comprising a frame delimiting a strung surface forming a mesh, a handle extending the frame outside the mesh, characterised in that the frame is formed, at least in a peripheral region, from a bent lamination of at least two layers of different materials placed adjacent to each other, the lamination being shaped so that, in a closed cross-section of said peripheral region, considered perpendicular to the neutral axis of the frame, the centre of mass of said cross-section is offset towards the mesh relative to the centre of area of said cross-section, by a value of at least 5% of the width of said cross-section, said width being defined by the intersection of the cross-section with the plane of the mesh.

A tennis racket formed in this way offers excellent performance in terms of handling, weight, mechanical strength, ability to stabilise the frame on large deformations and ability to filter micro-vibrations. A layer of a rigid, structural material on which one or more layers of materials with the aforementioned stabilising and filtering effects can rest is positioned towards the mesh. A central layer is for example intended to stabilise the frame on large vibrations while an outer layer, located away from the mesh, is capable of filtering micro-vibrations. The denser and therefore heavier (by unit of area of the cross-section) layers are located closest to the mesh, which limits the inertia effects relative to a longitudinal axis of the racket, or even relative to the gripping handle of the racket. Conversely, the less dense and therefore lighter (by unit of area of the cross-section) layers are located on the outer periphery of the frame, on the side furthest from the mesh. These layers are preferably intended to provide good compressive strength of the frame, stabilisation on large deformations and filtration of micro-vibrations.

Moreover, the layers of a racket frame according to the invention are advantageously made from wood (with the exception of an optional reinforcing sheath placed around one of the layers). The frame according to the invention formed in this way uses over 75% natural and renewable materials, which constitutes a particularly strong technical, ecological and commercial argument.

According to further advantageous features of the invention, the frame is formed from a lamination comprising at least two layers of different materials, a first layer of which, located on the inner side of the frame, has a greater density than the second layer, located on the outer side of the frame.

According to further advantageous features of the invention, the lamination is formed from at least three layers of at least two different materials.

According to further advantageous features of the invention, the lamination is formed from at least four layers of at least three different materials.

According to further advantageous features of the invention, the lamination comprises several layers of different types of wood, said types of wood being chosen from acacia, balsa and walnut.

According to further advantageous features of the invention, the lamination comprises at least one acacia layer located on the inner side of the frame and delimiting the mesh. Acacia is a wood with excellent mechanical properties. It is a highly responsive and resilient wood. Placed on the inner periphery of the mesh, it forms an excellent support for one of more layers located on the opposite side to the mesh, and due to its density in relation to the other layers, it makes it possible to move the centre of mass of the cross-section towards the centre of the mesh. As an optional variant, said at least one acacia layer can be formed of two acacia layers. Said two layers can be arranged so that their fibres are facing in the same direction or, conversely, in another optional variant of the invention, so that their respective fibres are facing in opposite directions.

According to further advantageous features of the invention, the lamination comprises at least one walnut layer located on the outside of the frame. Walnut is a low-density wood with cross-grain, which gives it an ability to filter micro-vibrations effectively.

According to further advantageous features of the invention, the lamination comprises at least one balsa layer. This material is appreciated for its great lightness.

According to further advantageous features of the invention, said at least one balsa layer is inserted between said at least one acacia layer and said at least one walnut layer. Said balsa core has great compressive strength and forms an excellent stabiliser on large deformations.

According to further advantageous features of the invention, said at least one balsa layer is encased in a sheath made from fibreglass or carbon or a mixture of both. Said sheath contributes to the rigidity and cohesion of all of the adjacent layers.

According to further advantageous features of the invention, the fibreglass sheath comprises a reinforcement selected from carbon threads or basalt threads.

According to further advantageous features of the invention, the layers are bonded together by polymerisation of a synthetic resin.

According to further advantageous features of the invention, the layers of wood of the lamination represent substantially the following proportions in the width of the cross-section:

-   -   between 20 and 40% acacia,     -   between 30 and 50% balsa,     -   between 20 and 40% walnut.

According to further advantageous features of the invention, the racket is a tennis racket.

The invention will be more clearly understood on reading the following description of a non-limitative embodiment of the invention and with reference to the attached drawings, in which:

FIG. 1 is a partial view of a tennis racket laid flat,

FIGS. 2 and 3 show a cross-section of the frame of the racket in FIG. 1 along the line A-A, in perspective and perpendicular to the plane of the cross-section respectively, and

FIG. 4 is a perspective view of a longitudinal portion of the balsa layer and its composite sheath.

FIG. 1 shows the frame of a tennis racket without its handle. Conventionally, the frame 1 delimits a strung surface forming a mesh 2. In the attached figures, the racket is shown without strings. The handle 3 is connected to the frame by two connecting arms 4, 5 as shown. In a variant (not shown), the handle 3 can be connected to the frame 1 by a single central arm.

According to an essential aspect of the invention and with reference to FIGS. 1 to 3, the frame 1 is formed, at least in a peripheral region, from a bent lamination of at least two layers 6-10 of different materials placed adjacent to each other, the lamination being configured so that, in a closed cross-section T of said peripheral region, considered perpendicular to the neutral axis of the frame 1, the centre of mass M of said cross-section T is offset towards the mesh 2 relative to the centre of area S of said cross-section T, by a value of at least 5% of the width L of said cross-section T, said width being defined by the intersection of the cross-section T with the plane of the mesh 2.

The cross-section is said to be “closed” in the sense that such a cross-section is only considered along a line A-A on one side of the frame 1 only, and not on both diametrically opposite sides. The centre of mass is defined as the centre of weight or barycentre of the cross-section. Said centre of mass takes into account differences in density, or more accurately relative mass, in each area or region of the cross-section. The centre of area is a geometric notion that corresponds to the centre of mass if the entire cross-section were fictitiously homogeneous, i.e. made from the same material with the same density or mass per unit of area in all regions.

In particular embodiments of the invention, this offset can for example be 10% or 20% or even more.

It must also be noted that an offset of the same magnitude is provided between the centre of mass M of the cross-section T and the neutral axis of the frame 1, the neutral axis conventionally being defined in that it forms a fictitious line in which the tensile or compressive forces are theoretically zero despite the bending of the frame.

In the particular embodiment of the invention shown in FIGS. 1 to 3, provision is made for the frame 1 to be formed homogeneously whatever the peripheral region considered. The cross-sections are thus formed in the same way at any point on the periphery of the frame 1. The adjacent layers 6-9 therefore have a substantially annular shape corresponding to the general shape of the frame 1.

According to the above definition of the invention, it will be understood in other words that the frame is configured so that, in at least one peripheral region, the mass or weight of the frame is substantially concentrated towards the mesh, i.e. towards the inside of the frame 1 rather than towards the outside. In the example shown in FIGS. 1 to 3, the frame is configured so that said concentration of mass or weight is provided evenly over the entire periphery thereof.

The frame 1 is thus formed from a lamination comprising at least two layers 6-9 of different materials, a first layer of which, located on the inner side of the frame, has a greater density than the second layer, located on the outer side of the frame.

In the example shown, the frame 1 is formed from a lamination with four layers 6-9 of three different materials. Said materials are advantageously wood. The types of wood are selected from acacia, balsa, walnut. Said types of wood are bonded and bent in a conventional manner known to a person skilled in the art of wooden rackets. In particular, the layers of wood are oven-bonded together by polymerisation of a synthetic resin.

In the embodiment shown, the two layers 6, 7 located on the inner side of the frame 1, i.e. adjacent to the mesh 2, are preferably acacia. As acacia is an extremely responsive, resilient wood, arranging it on the inner side of the mesh 2 turns it into a support or bearing element for the other two layers 8, 9, which are placed adjacent to it on the outer side from the mesh 2. As acacia is relatively dense, arranging it on the inner side of the mesh 2 makes it possible to reduce the polar inertia due to the distance of the masses from the centre of the mesh 2.

The two acacia layers are arranged so that their respective fibres are in opposite directions to each other. The layers are thus arranged head to toe. This arrangement increases the rigidity of the two acacia layers, which limits the deformation thereof.

The laminated frame 1 also comprises a walnut layer 9 located on the outside of the frame, at least on the outer side in relation to the acacia layers 6, 7. Walnut is a low-density wood with cross-grain, which gives it an ability to filter micro-vibrations effectively.

The frame 1 of the racket also comprises a balsa layer 8. This is inserted between the two acacia layers 6, 7 and the walnut layer 9. Said balsa core has great compressive strength and forms an excellent stabiliser on large deformations.

In an equally advantageous manner, the balsa layer 8 is encased in a fibreglass sheath 10, which can be seen in FIGS. 2 to 4. Said sheath contributes to the rigidity and cohesion of all of the adjacent layers. The sheath 10 is arranged around the balsa layer 8 in such a way as to form a reinforced central layer. The acacia layers 6, 7 and walnut layer 9 are then placed on either side of said reinforced central balsa layer 8, 10 prior to bending and bonding.

Optionally and in no way limitatively, the fibreglass sheath 10 comprises a reinforcement selected from carbon threads or basalt threads.

Considering the thicknesses of each wooden layer 6-9 relative to the width L of the cross-section T, the racket frame 1 according to the invention is proportionally defined as follows:

-   -   between 20 and 40% of the width L is acacia (all layers         combined),     -   between 30 and 50% of the width is balsa,     -   between 20 and 40% of the width is walnut.

As shown in FIG. 2, the frame has a cross-section T with the general shape of a rectangle with rounded edges. The layers 6-9 are oriented parallel to the long sides of the rectangle. Thus, the frame 1 leaves visible the edges of the different layers 6-9 on the opposite parallel faces thereof, which correspond to the short sides of the rectangle. It will also be noted that the rectangle is deformed/domed on the inner side, i.e. on the side of the mesh 2. The two acacia layers 6, 7 can therefore be of different thicknesses and shapes.

Of course, the invention is not limited to the embodiments described above and includes all technical equivalents.

For example, a variant embodiment of the invention can comprise a single acacia layer on the inner side of the frame 1. Provision can also be made for at least two balsa layers or at least two walnut layers on the outer side of the frame 1. 

1. Racket for ball games, particularly tennis, comprising a frame delimiting a strung surface forming a mesh, a handle extending the frame outside the mesh, characterised in that the frame is formed, at least in a peripheral region, from a bent lamination of at least two layers of different materials placed adjacent to each other, the lamination being shaped so that, in a closed cross-section of said peripheral region, considered perpendicular to the neutral axis of the frame, the centre of mass of said cross-section is offset towards the mesh relative to the centre of area of said cross-section, by a value of at least 5% of the width of said cross-section, said width being defined by the intersection of the cross-section with the plane of the mesh.
 2. Racket according to claim 1, characterised in that the frame is formed from a lamination comprising at least two layers of different materials, a first layer of which, located on the inner side of the frame, has a greater density than the second layer, located on the outer side of the frame.
 3. Racket according to claim 1, characterised in that the lamination is formed from at least three layers of at least two different materials.
 4. Racket according to claim 1, characterised in that the lamination is formed from at least four layers of at least three different materials.
 5. Racket according to claim 1, characterised in that the lamination comprises several layers of different types of wood, said types of wood being selected from acacia, balsa, walnut.
 6. Racket according to claim 5, characterised in that the lamination comprises at least one acacia layer located on the inner side of the frame and delimiting the mesh.
 7. Racket according to claim 5, characterised in that said at least one acacia layer is formed from two acacia layers arranged so that the respective fibres thereof are in opposite directions to each other.
 8. Racket according to claim 5, characterised in that the lamination comprises at least one walnut layer located on the outside of the frame.
 9. Racket according to claim 5, characterised in that the lamination comprises at least one balsa layer.
 10. Racket according to claim 9, characterised in that said at least one balsa layer is inserted between said at least one acacia layer and said at least one walnut layer.
 11. Racket according to claim 9, characterised in that said at least one balsa layer is encased in a fibreglass sheath.
 12. Racket according to claim 11, characterised in that the fibreglass sheath comprises a reinforcement selected from carbon threads or basalt threads.
 13. Racket according to claim 1, characterised in that the layers are bonded together by polymerisation of a synthetic resin.
 14. Racket according to claim 5, characterised in that the wooden layers of the lamination represent substantially the following proportions in the width of the cross-section: between 20 and 40% acacia, between 30 and 50% balsa, between 20 and 40% walnut.
 15. Racket according to claim 1, characterised in that it is a tennis racket. 